A digital recording and reproducing apparatus for recording transmitted digital image data and digital audio data onto a recording medium such as a magnetic tape or the like and for reproducing the digital data recorded on the recording medium has been known.
An example of a block diagram of such a digital recording and reproducing apparatus is shown in FIG. 1. In FIG. 1, in a recording system of digital data, digital data transmitted via an input terminal 101 is subjected to a predetermined process in a recording processing circuit 102. A parity having a product code construction generated by a parity generating circuit 103 is added to output data of the recording processing circuit 102. In a sync and ID generating circuit 104, a sync code and an ID are added to the data to which the parity was added. Output data of the sync and ID generating circuit 104 is subjected to a parallel/serial conversion and a conversion to a recording code in a channel encoder 105. After the data is amplified by an amplifier 106, the data is recorded on a magnetic tape 109 through a recording side terminal R of a switch 107 and a magnetic head 108.
In a reproduction system of image data and audio data in a digital recording and reproducing apparatus, the recording data recorded on the magnetic tape 109 is supplied to an amplifier and equalizer 110 through the magnetic head 108 and a reproducing side terminal (P) of the switch 107 and is subjected to an amplification and a correction of frequency characteristics. Output data of the amplifier and equalizer 110 is subjected to a decoding of a recording code and a serial/parallel conversion in a channel decoder 111 and is supplied to a sync and ID detecting circuit 112. In the sync and ID detecting circuit 112, a sync code and the ID in the data are detected and supplied to a TBC (Time Base Corrector) circuit 113 together with the reproduction data. In the TBC circuit 113, a time base fluctuation for the data is eliminated. Output data of the TBC circuit 113 is subjected to an error correcting process using a product code in an ECC circuit 114 and, after that, the data is supplied to an output terminal 116 through a reproduction processing circuit 115.
A tape format of the digital recording and reproducing apparatus has, for example, a construction as shown in FIG. 2. That is, from the scanning direction (left edge) of a head (not shown) of the digital recording and reproducing apparatus, the tape format is constructed in accordance with the order of a margin area 1, an ATF and timing sync area, an IBG (inter block gap) area 1, an audio data area, an IBG area 2, a video data area, an IBG area 3, a subcode area, and a margin area 2. The ATF and timing sync area is an area in which data for tracking and data to obtain a synchronization when after-recording are recorded. Between the above-mentioned areas, an amble area is inserted.
IBG is provided as an area to assure a margin for after-recording. Data is not recorded in the IBG. For example, a pulse signal of a frequency which is equal to a bit frequency of the recording data is recorded in each amble area. The pulse signal is used to lock a PLL circuit for a bit clock extraction provided on the reproduction side. Margin 1 and margin 2 are areas to cope with a case where a forming position of the track changes by a jitter.
The magnetic tape for the digital recording and reproducing apparatus is scanned by heads shown in FIGS. 3A, 3B and 3C. According to the heads shown in FIG. 3A, four heads in which a head A1 and a head B0 face each other and a head B1 and a head A0 correspond to each other are attached to a drum (D). According to the head shown in FIG. 3B, magnetic heads A0 and B0 are attached to a rotary drum (D) in a manner such that the magnetic head A0 faces the magnetic head B0 by 180.degree.. The head shown in FIG. 3C relates to an example in which the magnetic heads A0 and B0 are attached to the rotary drum (D) so as to be arranged at extremely near positions. Such a magnetic head is integratedly constructed and is called a double azimuth head.
Although not shown, the magnetic tape is wound around the peripheral surface of the drum (D) with a wrap angle which is slightly larger than 180.degree. and is fed at a constant speed. A digital video signal is sequentially recorded as an oblique track on the magnetic tape by the magnetic heads A0 and B0. In order to suppress the crosstalk between the neighboring tracks, an extending direction of the gap between the magnetic heads A0 and A1 and an extending direction of the gap between the heads B0 and B1 are made different by a predetermined angle. Thus, the crosstalk between the neighboring tracks can be reduced by the azimuth loss which occurs when reproducing.
When the drum (D) is rotated 9000 times per one minute and the magnetic tape is run at a standard speed (for example, 18.8 mm/sec), the data is recorded at a predetermined position on the tape by the heads. For the recording of the video data of one frame, for instance, 10 tracks are allocated.
For a video data area on the magnetic tape, the video data is recorded at a recording rate of 24.948 Mbps in the normal recording mode (hereinafter, referred to as an SD mode). When the recording is performed in a variable speed recording mode, for example, at a speed which is two times as high as that of the normal recording mode (hereinafter, referred to as an HD mode), data is recorded at a recording rate of 49.896 Mbps. The recording (long-time mode) at a recording data rate (12.474 Mbps) which is 1/2 of the data rate of the recording used in the SD mode is also considered. Further, a digital recording and reproducing apparatus for recording data compressed to various data rates in a range from about 1 Mbps to 10 Mbps is also considered.
When the video data which is supplied at a different data rate, for example, the video data of 5 Mbps is recorded at a recording rate of the above-mentioned long-time mode, superfluous data is recorded in the video data area of about 7.5 Mbps (12.474 Mbps-5 Mbps). That is, although the video data of 12.474 Mbps can be inherently recorded in the video data area, only the data area that is equal to or less than the half of the video data area is actually used. By recording superfluous data, the recordable time of the magnetic tape is reduced.
In case of recording general data (discontinuous data such as a computer program or the like) in which errors cannot be corrected with respect to the space or time, it is necessary to verify whether the correct recording has been performed or not. An exclusive-use head other than the recording head is needed for the above verification, so that problems of a complication of a head construction and an increase in costs occur.
The invention is made in consideration of the problems as mentioned above and an object of the invention is, therefore, to provide a recording and reproducing apparatus in which digital video data, computer data, and general data (shopping data, newspaper data, or the like) which is digitally transmitted can be recorded at an optimum data rate, so that the recordable time can be increased.
Another object of the invention is to provide a recording and reproducing apparatus in which when data at a low rate is intermittently recorded, whether the immediately preceding recording has correctly been performed or not can be verified without requiring a special head.